Semiconductor laser element and method of making semiconductor laser device

ABSTRACT

A semiconductor laser element includes an inclined substrate, a semiconductor layer formed on one surface of the substrate, a first electrode (n-type electrode) formed on an opposite surface of the substrate, a second electrode (p-type electrode) formed on the semiconductor layer, and a current constriction part formed in the semiconductor layer. The semiconductor layer has a multi-layer structure including at least an active layer. The current constriction part causes a current to concentrate and flow to a particular area of the active layer. The first electrode or the second electrode is joined to a sub-mount. In one embodiment, the location of the current constriction part in a chip width direction is between the center of one of the first and second electrodes, which is joined to the sub-mount, and the center of the other electrode, which is not joined to the sub-mount, when viewed in the chip width direction.

FIELD OF THE INVENTION

The present invention relates to a semiconductor laser element (laserdiode) and a method of manufacturing a semiconductor laser device.

DESCRIPTION OF THE RELATED ART

Conventionally, an edge emitting semiconductor laser element usually hasa GaAs substrate, an InP substrate, a GaN substrate, an Si substrate orthe like. In case of a red laser diode (LD), for example, anAlGaInP-based crystal is grown on a GaAs substrate by a MOCVD (MetalOrganic Chemical Vapor Deposition) method or a similar method.

However, when the GaAs substrate is used, AlGaInP forms a naturalsuperlattice. If the AlGaInP-based crystal is grown on the GaAssubstrate, a band-gap energy is larger when group III atoms aredisorderly arranged and form the natural superlattice than when groupIII atoms are orderly (regularly) arranged and form the naturalsuperlattice if the crystal composition is the same. The light emissionwavelength of the semiconductor laser element is decided by the band-gapenergy of an active layer. In order to obtain a laser beam at a shortwavelength, therefore, the active layer needs to have a large band-gapenergy.

When AlGaInP is grown on a substrate crystal, and a plane orientation(plane direction) of a principal plane (surface) of the substratecrystal is inclined in a particular direction, then the formation of thenatural superlattice is suppressed, and the resulting crystal can have alarge band-gap energy even if the composition is the same. This is knownin the art. For example, Japanese Patent Application Laid-openPublication No. Hei 11-274635 discloses a semiconductor laser elementthat uses a canted GaAs substrate (inclined substrate). The planeorientation of the GaAs substrate is inclined by 5-15 degrees from the(100) plane.

SUMMARY OF THE INVENTION

In recent years, there is a demand for a semiconductor laser that canprovide a higher optical output, and the length of a chip cavity(resonator length) becomes longer. However, if the cavity length becomeslonger, the number of chips to be obtained from a single waferdecreases. This increases a manufacturing cost. To avoid this, a chipwidth that is measured in a direction perpendicular to the cavitydirection of the chip is reduced such that a certain number of chips areobtained from a single wafer.

However, the inclined substrate disclosed in Japanese Patent ApplicationLaid-open Publication No. Hei 11-274635 is used in the chip having anarrow width, the method of manufacturing the semiconductor laser deviceencounters some problems when the chip is joined to (mounted on) asub-mount. For example, when the chip is joined to the sub-mount, and anexcessive load is applied onto the chip in order to improve thewettability to solder, then the chip may tilt, fall, collapse or breakbecause the chip width is small. If the chip tilts, the heat dissipationmay drop and/or the polarization performance drop because ofinsufficient wettability. This deteriorates the reliability of theresulting product (laser device). On the other hand, if a load isreduced in order to prevent the tilting of the chip and the breakage ofthe chip, then the chip is not wet with the solder, and the heatdissipation decreases. This also deteriorates the reliability of theresulting product.

The present invention is proposed to overcome the above-describedproblems, and an object of the present invention is to provide asemiconductor laser element that is joined to a sub-mount in a desiredmanner even when the inclined substrate is used and the width of thesubstrate is relatively small in the direction perpendicular to thecavity direction.

Another object of the present invention is to provide a method ofmanufacturing a laser device that includes such semiconductor laserelement.

According to an aspect of the present invention, there is provided asemiconductor laser element that includes a semiconductor chip. Thesemiconductor chip has a substrate. The substrate has four side faces, atop face and a bottom face. Two of the four side faces are inclined sidesurfaces which face each other in a first direction, and another twoside faces are vertical side surfaces which face each other in a seconddirection. The second direction is perpendicular to the first direction.Each vertical side surface has a parallelogram shape. The semiconductorchip also has a semiconductor layer formed on one of the top and bottomfaces of the substrate, a first electrode formed on the other of the topand bottom faces of the substrate, and a second electrode formed on thesemiconductor layer. The semiconductor layer has a multi-layer structureincluding at least an active layer. The semiconductor chip also has acurrent constriction part formed in the semiconductor layer. The currentconstriction part causes the current to concentrate and flow to aparticular area of the active layer. The first electrode or the secondelectrode (the top or bottom face of the substrate) will be joined to asub-mount when the semiconductor laser element is assembled in a laserdevice. The location of the current constriction part in the firstdirection is offset from the center of one of the top and bottom facesof the substrate, on which the electrode (first or second electrode) tobe joined to the sub-mount is formed, toward the center of the other ofthe top and bottom faces of the substrate, when viewed in the chip widthdirection.

When the semiconductor laser element is joined to the sub-mount, thesemiconductor laser element is placed on the sub-mount and then a forceis applied onto the semiconductor laser element. Usually, the force isapplied onto the semiconductor laser element between the center of thatface (the top or bottom face) of the chip, which will be joined to thesub-mount, and the center of the opposite face of the chip, when viewedin the chip width direction. Because the current constriction part isformed at a position offset from the center of one of the top and bottomfaces of the substrate, on which the electrode (first or secondelectrode) to be joined to the sub-mount is formed, toward the center ofthe other of the top and bottom faces of the substrate, when viewed inthe chip width direction, a relatively small force is enough to join thechip to the sub-mount in a desired manner (enough to ensure the wettingof the chip with the solder). Accordingly, even when the width of thesubstrate of the semiconductor laser element is small in a directionperpendicular to the cavity direction and the semiconductor laserelement has the inclined substrate, it is still possible to prevent thechip from leaning (tilting), falling, collapsing and/or breaking whenthe chip is joined to the sub-mount.

The location of the current constriction part in the first direction maybe on a line that extends through the center of gravity of thesemiconductor chip when viewed in the first direction.

The semiconductor laser element may be suction-held by a collet or thelike in order to convey the semiconductor laser element to the sub-mountand join the semiconductor laser element to the sub-mount. In order forthe collet to catch and hold the semiconductor laser element in a stablemanner, the collet firstly approaches the semiconductor laser elementalong the line extending through the center of gravity of thesemiconductor laser element, and the collet contacts and catches thesemiconductor laser element. When the collet joins the semiconductorlaser element to the sub-mount, the collet may apply a joining forceonto the semiconductor laser element while the collet is contacting thesemiconductor laser element in the same manner as the collet catches andholds the semiconductor laser element. When the location of the currentconstriction part is on the line that extends through the center ofgravity of the semiconductor laser element, it is possible to join thesemiconductor laser element to the sub-mount with a relatively smallforce in a desired manner.

Alternatively, the location of the current constriction part in thefirst direction may be on a line that extends through the center of oneof the first and second electrodes which will not be joined to thesub-mount when viewed in the first direction (chip width direction).

Alternatively, the location of the current constriction part in thefirst direction may be on a line that extends through the center of thatface of the chip, on which the electrode (first or second electrode) notto be joined to the sub-mount is provided, when viewed in the firstdirection (chip width direction).

When the collet catches and holds, by suction, the semiconductor laserelement to convey the semiconductor laser element to the sub-mount, thecollet may firstly approach the semiconductor laser element along thecenter line of that face of the semiconductor laser element which willnot be joined to the sub-mount until the collet contacts and catches thesemiconductor laser element. When the collet joins the semiconductorlaser element to the sub-mount, the collet may apply a joining forceonto the semiconductor laser element while the collet is contacting thesemiconductor laser element in the same manner as the collet catches andholds the semiconductor laser element. When the location of the currentconstriction part is on the line that extends through the center of theface of the semiconductor laser element which is not joined to thesub-mount, as viewed in the chip width direction, it is possible to jointhe semiconductor laser element to the sub-mount with a relatively smallforce in a desired manner.

The current constriction part of the semiconductor laser element mayhave a ridge structure. The current constriction part having the ridgestructure can provide good light output characteristics.

The current constriction part of the semiconductor laser element mayhave a plurality of ridges arranged in the first direction. A centerposition of the ridges in the first direction may be the location of thecurrent constriction part in the first direction. With thisconfiguration, it is possible to appropriately join the semiconductorlaser element to the sub-mount even when the current constriction parthas a plurality of ridges.

The first electrode of the semiconductor laser element may be theelectrode that will not be joined to the sub-mount, and the secondelectrode may be the other electrode that will be joined to thesub-mount. This is called a junction down method. As the semiconductorlaser element (the second electrode) is joined to the sub-mount by thejunction down method, the heat dissipation of the semiconductor laserelement is improved.

According to another aspect of the present invention, there is provideda method of manufacturing a semiconductor laser element. Thesemiconductor laser element manufacturing method includes preparing asubstrate. The substrate has four side faces, a top face and a bottomface. Two side faces of the four side faces are inclined side surfaceswhich face each other in a first direction, and another two side facesare vertical side surfaces which face each other in a second direction.The second direction is perpendicular to the first direction. Eachvertical side surface has a parallelogram shape. The semiconductor laserelement manufacturing method also includes forming a semiconductor layeron one of the top and bottom faces of the substrate. The semiconductorlayer has a multi-layer structure including at least an active layer.The semiconductor laser element manufacturing method also includesforming a first electrode formed on the other of the top and bottomfaces of the substrate. The semiconductor laser element manufacturingmethod also includes forming a second electrode formed on thesemiconductor layer. The semiconductor laser element manufacturingmethod also includes forming a current constriction part in thesemiconductor layer. The current constriction part is configured tocause a current to concentrate and flow to a particular area of theactive layer. The location of the current constriction part in the firstdirection is offset from a center of that face (the top or bottom face)of the chip, on which the electrode (the first or second electrode) tobe joined to a sub-mount is provided toward the center of the oppositeface of the substrate, when viewed in the chip width direction.

With this semiconductor laser element manufacturing method, it ispossible to provide a semiconductor laser element that can appropriatelybe joined to the sub-mount with a relatively small force. Even when theinclined substrate is used and the width of the inclined substrate issmall in a direction perpendicular to the cavity direction, it is stillpossible to manufacture a semiconductor laser element having highreliability that does not tilt, fall, collapse and/or break when thesemiconductor laser element is joined to the sub-mount.

According to still another aspect of the present invention, there isprovided a method of manufacturing a semiconductor laser device. Thesemiconductor laser device manufacturing method includes preparing asemiconductor laser element according to one of the aspects of thepresent invention as described above. The semiconductor laser devicemanufacturing method also includes placing the semiconductor laserelement on the sub-mount such that one of the first and secondelectrodes faces or contacts the sub-mount. The semiconductor laserdevice manufacturing method also includes applying a force onto thesemiconductor laser element in a direction perpendicular to a joiningplane between said one of the first and second electrodes and thesub-mount so as to join the semiconductor laser element to thesub-mount. With this semiconductor laser device manufacturing method, itis possible to provide a semiconductor laser device having highreliability in which the semiconductor laser element is appropriatelyjoined to the sub-mount.

According to yet another aspect of the present invention, there isprovided a method of manufacturing a semiconductor laser device. Thesemiconductor laser device manufacturing method includes preparing asemiconductor laser element. The semiconductor laser element includes asubstrate, a semiconductor layer, a first electrode, a second electrode,and a current constriction part. The substrate has four side faces, atop face and a bottom face. Two side faces of the four side faces areinclined side surfaces which face each other in a first direction, andanother two side faces are vertical side surfaces which face each otherin a second direction. The second direction is perpendicular to thefirst direction. Each vertical side surface has a parallelogram shape.The semiconductor layer is formed on one of the top and bottom faces ofthe substrate. The semiconductor layer has a multi-layer structureincluding at least an active layer. The first electrode is formed on theother of the top and bottom faces of the substrate. The second electrodeis formed on the semiconductor layer. The current constriction part isformed in the semiconductor layer. The current constriction part isconfigured to cause a current to concentrate and flow to a particulararea of the active layer. The semiconductor laser device manufacturingmethod also includes placing the semiconductor laser element on asub-mount such that one of the first and second electrodes contacts orfaces the sub-mount. The semiconductor laser device manufacturing methodalso includes applying a force onto the semiconductor laser element in adirection perpendicular to a joining plane between said one of the firstand second electrodes and the sub-mount from above the currentconstriction part, so as to join the semiconductor laser element to thesub-mount. With this semiconductor laser device manufacturing method,the semiconductor laser element is appropriately joined to thesub-mount, and the semiconductor laser device has high reliability.

The semiconductor laser element (semiconductor laser chip) of theinvention can prevent the tilting of the semiconductor laser chip, thefalling of the semiconductor laser chip, and the breaking of thesemiconductor laser chip when the semiconductor laser chip is joined tothe sub-mount even if the inclined substrate is used and the width ofthe inclined substrate is relatively small in a direction perpendicularto the cavity direction. Thus, it is possible to join the semiconductorlaser chip to the sub-mount in a desired manner. Accordingly, thereliability of a resulting product (laser device) that includes thesemiconductor laser element is ensured, and the semiconductor laserelement (laser device) can emit light having a higher optical output ata shorter wavelength.

These and other objects, aspects and advantages of the present inventionwill become apparent to those skilled in the art from the followingdetailed description when read and understood in conjunction with theappended claims and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view that shows an exemplary configurationof a semiconductor chip according to a first embodiment of the presentinvention.

FIG. 2 is a view useful to describe a method of manufacturing asemiconductor laser device.

FIG. 3 is a view useful to describe the method of manufacturing thesemiconductor laser device.

FIG. 4 is a view useful to describe the method of manufacturing thesemiconductor laser device.

FIG. 5 is a view useful to describe the method of manufacturing thesemiconductor laser device.

FIG. 6 is a cross-sectional view that shows an exemplary configurationof a semiconductor chip according to a second embodiment of the presentinvention.

FIG. 7 is a cross-sectional view that shows an exemplary configurationof a semiconductor chip according to a third embodiment of the presentinvention.

FIG. 8 is a cross-sectional view that shows an exemplary configurationof a semiconductor chip according to a fourth embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Now, embodiments of the present invention will be described withreference to the accompanying drawings.

First Embodiment

Referring to FIG. 1, an exemplary configuration of a semiconductor chip10, which serves as a semiconductor laser element of this embodiment,will be described.

The semiconductor chip (hereinafter simply referred to as “chip”) 10 ofthe semiconductor laser element oscillates to emit a laser beam when thechip is assembled into a semiconductor laser device and is supplied witha predetermined injection current. The chip 10 has a semiconductorsubstrate 11. The substrate 11 is an inclined substrate (inclinationangle is θ). A semiconductor layer having a multi-layer structure isformed on a principal surface of the semiconductor substrate 11 byepitaxial growth. The semiconductor substrate 11 is, for example, ann-GaAs substrate. The principal surface of the substrate 11 is inclinedat the predetermined inclination angle θ (e.g., 15 degrees) in the <011>direction from the (100) plane. Thus, the semiconductor substrate 11 hasa parallelepiped shape. The parallelepiped shape includes four sidefaces, a top face and a bottom face. The four side faces include twoinclined side faces, which face each other in a first direction(right-left direction in FIG. 1), and another two side faces or verticalfaces, which face each other in a second direction. The second directionis perpendicular to the first direction (vertical direction to thedrawing sheet of FIG. 1). The vertical face has a parallelogram shape,which includes a diamond shape. In the following description, thesemiconductor substrate 11 is occasionally referred to as “inclinedsubstrate.”

In this embodiment, the chip 10 oscillates to emit a laser beam at some600 nm wavelength when the chip 10 is assembled in a semiconductor laserdevice and supplied with a predetermined injection current. In thisembodiment, the thickness (height) of the inclined substrate 11, whichcorresponds to the thickness of the chip 10, is from 50 μm to 200 μm(e.g., 100 μm). The width of the inclined substrate 11, whichcorresponds to the width of the chip 10, in the first direction is equalto or less than 150 μm (e.g., 100 μm). The inclination angle θ is from 3degrees to 20 degrees (e.g., 15 degrees). In this embodiment, the lengthof the chip 10 (resonator length) in the second direction is from 300 μmto 3000 μm (e.g., 2000 μm).

The semiconductor layer includes an active layer 12 (e.g., GaInP layer).Specifically, the semiconductor layer has, at least, a firstconduction-type semiconductor layer, the active layer 12, and a secondconduction-type semiconductor layer. The semiconductor layer is formedon the lower face (bottom face) of the inclined substrate 11. The firstconduction-type semiconductor layer, the active layer 12, and the secondconduction-type semiconductor layer are stacked in this order. In FIG.1, the first conduction-type semiconductor layer is formed on an upperface of the active layer 12. The first conduction-type semiconductorlayer is an n-type cladding layer (e.g., n-AlGaInP layer). The secondconduction-type semiconductor layer is formed on a lower face of theactive layer 12 (formed under the active layer 12). The secondconduction-type semiconductor layer is a p-type cladding layer (e.g.,p-AlGaInP layer). The chip 10 has a p-type electrode (second electrode)13 formed under the semiconductor layer (on the bottom face of thesemiconductor layer), and an n-type electrode (first electrode) 14 ontop of the inclined substrate 11 (on the top face of the substrate). Inthis embodiment, the center of the p-type electrode 13 is aligned withthe center of that surface (bottom face) of the chip 10 which contactsthe p-type electrode 13. Likewise, the center of the n-type electrode 14is aligned with the center of that surface (top face) of the chip 10which contacts the n-type electrode 14.

A ridge portion 15 having a protrusion is formed on the lower surface ofthe chip 10, i.e., the ridge portion 15 is formed on that surface of thechip 10 which contacts the p-type electrode (p-type cladding layer) 13.The ridge portion 15 is a current constriction part that concentratesand injects the current in a particular area in the active layer 12which serves as a light emitting part. Thus, in FIG. 1, a point 16 inthe active layer 12 that corresponds to the ridge portion 15 becomes alight emitting point, and the light emitting point 16 emits a laserbeam.

The ridge portion 15 is formed on the line Pg that extends in adirection perpendicular to the first direction and the second direction(cavity direction) and that passes through the center of gravity 17 ofthe chip 10, as shown in FIG. 1. The line Pg is a vertical line to asurface that joins to the sub-mount 20 (will be described later). Inother words, the location of the ridge portion 15 in the first direction(chip width direction) corresponds to the position of the center ofgravity 17 of the chip 10 in the first direction. The line Pg is a linethat extends through the center of gravity 17 of the chip 10 in FIG. 1.

The chip 10 is joined to the sub-mount 20 of the semiconductor laserdevice. A main body of the sub-mount 20 is made from, for example,aluminum nitride (AlN). The material of the main body of the sub-mount20 is decided appropriately on the basis of the heat dissipation, theinsulation, the difference in the linear expansion coefficient betweenthe sub-mount and the semiconductor laser chip, the cost and the like.If the heat dissipation and the insulation are considered, the materialof the main body of the sub-mount 20 may be silicon carbide (SiC) ordiamond. If the conductivity is considered, the material of the mainbody of the sub-mount 20 may be Cu, CuW or CuMo. If the cost isconsidered, the material of the main body of the sub-mount 20 may be Sior aluminum oxide (Al₂O₃). It should be noted that the main body of thesub-mount 20 may made from a combination of the insulation material,such as SiC, and the conductive material, such as Cu. An electrodewiring 21 is formed on the surface of the sub-mount 20. The material ofthe electrode wiring 21 is gold (Au). The chip 10 is joined onto theelectrode wiring 21 by a junction down method with, for example,gold-tin (AuSn) solder 22. The surface of the p-type electrode 13 (i.e.,the light emitting surface of the chip 10, or the active layer 12 sidesurface of the chip 10) serves as a joining surface to the sub-mount 20.Thus, the p-type electrode 13 is electrically connected to the electrodewiring 21 of the sub-mount 20. The bonding material to the surface ofthe sub-mount 20 may be solder, such as tin-silver-copper (SnAgCu),tin-silver (SnAg), or tin-gold (SnAu), or a metallic material having alow melting point, such as indium (In) or silver (Ag) paste. The n-typeelectrode 14 is connected to an electrode (not shown), which is providedto feed the injunction current, by wiring (Au wire) 23, and theelectrode wiring 21 is connected to another electrode (not shown), whichis provided to feed the injection current, by wiring (Au wire) 24. Thediameter of each of the Au wires 23 and 24 is, for example, 25 μm.

It should be noted that the location of the ridge portion 15 in the chipwidth direction is not limited to “on the line Pg” that corresponds tothe center of gravity 17 of the chip 10 in the chip width direction. Itis satisfactory as long as the location of the ridge portion 15 in thechip width direction is offset from the line Pp toward the line Pn. Inother words, it is satisfactory as long as the location of the ridgeportion 15 in the chip width direction is on the right side of the linePp in FIG. 1. The line Pn extends through the center of the top face ofthe substrate 11 on which the electrode 14 is formed. This is betweenthe center position of that surface (lower surface or the p-typeelectrode 13 surface) of the chip 10 which is joined to the sub-mount 20and the center position of the opposite surface of the chip which is notjoined to the sub-mount 20 when viewed in the chip width direction.

In this embodiment, therefore, the location of the ridge portion 15 inthe chip width direction is on the right side of the center line Pp ofthat surface of the chip which contacts the sub-mount 20 when viewed inthe chip width direction. Preferably, the location of the ridge portion15 in the chip width direction is between the center line Pp of thep-type electrode 13 and the center line Pn of the n-type electrode 14.

Now, a method of manufacturing the semiconductor laser device will bedescribed.

Firstly, as shown in FIG. 2, the chip 10 is suctioned by a collet 30 bymeans of vacuum suction, and the chip 10 is conveyed to a predeterminedposition above a sub-mount 20 by the collet 30. Then, the collet 30 islowered to place the chip 10 on the sub-mount 20 as indicated by thearrow X1. When the collet 30 catches the chip 10, the collet 30approaches the chip 10 while moving along the line Pg that passesthrough the center of gravity of the chip 10. The collet 30 catches andholds an n-type electrode 14 of the chip 10. After catching the chip 10,the collet 30 conveys the chip 10 to the sub-mount 20, as shown in FIG.3, while moving down as shown by the arrow X2. After the collet 30places the chip 10 on the sub-mount 20, as shown in FIG. 4, the collet30 exerts a load (joining force) X3 onto the chip 10 (more precisely,the n-type electrode 14 of the chip 10) in a direction perpendicular tothe joining surface. The collet 30 exerts the load X3 along the line Pg,i.e., the collet 30 exerts the force X3 on the chip 10 at a position ofthe vacuum suction. The force X3 exerted by the collet 30 is fromapproximately 3 g to 60 g, and preferably from approximately 10 g to 30g. For example, the force X3 exerted by the collet 30 is 20 g. When thegold-tin solder is used to join the chip 10 to the sub-mount 20, thesolder is heated to 280 degrees C. or higher. In this manner, the chip10 is joined to the sub-mount 20 with the solder+.

After the chip 10 is joined to the sub-mount 20, the chip 10 and thesub-mount 20 are joined to a disc-shaped stem 40 of a semiconductorlaser device 50, as shown in FIG. 5. The stem 40 has a heat sink 40 anear the center of the stem 40, and the sub-mount 20, on which the chip10 is mounted, is joined to the heat sink 40 a by solder 41. Thesub-mount 20 is attached to the heat sink 40 a such that the laser lightemitting direction of the chip 10 coincides with a direction vertical tothe disc-shaped surface of the stem 40.

The stem 40 may be made from an Fe alloy. Alternatively, the stem 40 maybe made from a gold-plated iron (Fe) or a gold-plated copper (Cu). Theheat sink 40 a may be made from a metal that has a good heat conductionsuch as copper (Cu). Leads 42 and 43 are secured to the stem 40 suchthat the leads 42 and 43 serve as the electrodes for feeding theinjunction current. The leads 42 and 43 are electrically insulated fromthe stem 40.

As the sub-mount 20 that carries the chip 10 thereon is mounted on theheat sink 40 a, the n-type electrode 14 (FIG. 1) is electricallyconnected to the lead 42 by the Au wire 23 by means of wire bonding, asshown in FIG. 5. The electrode wire 21 (FIG. 1) on the surface of thesub-mount 20 is electrically connected to the lead 43 by the Au wire 24by means of wire bonding. Thus, the electricity feeding to the p-typeelectrode 13 (FIG. 1) becomes possible.

Finally, a cylindrical cap 44 is placed over the disc-shaped surface ofthe stem 40, and the cap 44 is air-tightly joined to the stem 40 bywelding or the like. Thus, the heat sink 40 a of the stem 40, the leads42 and 43, the sub-mount 20, the chip 10 and the Au wires 23 and 24 arecovered with (received in) the cap 44. The cap 44 is made from, forexample, a metallic material, and protects the chip 10, the Au wires 23and 24, and other components that are received in the cap 44. The cap 44has a window (light transmitting window) 45 at the center of the topsurface of the cap 44 as an exit of the light (laser beam) emitted fromthe chip 10.

In this manner, the semiconductor laser device 50 is manufactured. Uponapplying a predetermined voltage across the leads 42 and 43 of thesemiconductor laser device 50, the laser beam is emitted from the edgeof the chip 10, and is radiated to the outside from the stem 40 throughthe light exit window 45.

In the method of manufacturing the semiconductor laser device 50 shownin FIG. 2 to FIG. 5, the chip 10 is mounted on the sub-mount 20, andthen the sub-mount 20, which carries the chip 10 thereon, is mounted onthe stem 40. It should be noted that the method of manufacturing thesemiconductor laser device 50 of the present invention is not limited inthis regard. For example, the sub-mount 20 may be joined to the heatsink 40 a of the stem 40, and then the chip 40 may be mounted on thesub-mount 20. Alternatively, the process of joining the sub-mount 20 tothe heat sink 40 a may be carried out at the same time when the processof joining the chip 10 on the sub-mount 20 is carried out. Joining thesub-mount 20 to the heat sink 40 a, and joining the chip 10 on thesub-mount 20 may be carried out in a single process.

As described above, the inclined substrate 11 is used as the substrateof the chip 10 in this embodiment. Because the inclined substrate 11 isused, the natural superlattice of AlGaInP, in which the group III atomsare arranged periodically (orderly), is eliminated, and the band gap canbe expanded. For example, in case of AlGaInP having the samecomposition, AlGaInP, in which the group III atoms are arrangeddisorderly, can expand the band gap by approximately 50 meV to 100 meVas compared to AlGaInP, in which the natural superlattice is formed.Accordingly, when the inclined substrate is used, it is possible to emita red laser beam in the short wavelength range (equal to or below 690nm; for example 640 nm). In addition, when the inclined substrate isused, a p-type dopant is easy to enter, and a high concentration dopingbecomes possible. Thus, it is possible to impart desired characteristicsto the semiconductor laser device and improve the quality of thecrystal. This contributes to an improvement in reliability of thesemiconductor laser element and the semiconductor laser device.

In this embodiment, the ridge portion 15 is provided as the currentconstruction part that causes the current to concentrate and flow to aparticular area of the active layer 12. The ridge structure makes itpossible to concentratedly feed the current to the particular area ofthe active layer 12 in an efficient manner, and convert the injectedcurrent into a laser beam in an efficient manner. Accordingly, thesemiconductor laser element can provide a higher optical output (canemit a high-power laser beam).

In this embodiment, the location of the ridge 15 in the chip widthdirection is “on the line Pg” that extends through the center of gravity17 of the chip 10 in the chip direction. Thus, the ridge 15 is formedjust below the center of gravity 17 of the chip 10, when viewed in thechip width direction. It is then possible to appropriately mount (join)the chip 10 on the sub-mount 20.

When the collet 30 catches the chip 10 to join the chip 10 to thesub-mount 20, it is necessary to pick up (lift) the chip 10 in a stablemanner. Then, it is necessary for the collet 30 to suck and hold thecenter of gravity of the chip 10. When the collet 30 places the chip 10on the sub-mount 20 and joins the chip 10 to the sub-mount 20, thecollet 30 applies the force onto the chip 10 while the collet 30 isholding the chip 10. Thus, the collet 30 applies the force to that areaof the chip 10 which is sucked and held by the collet 30.

In this embodiment, the ridge portion 15 is formed just below the centerof gravity 17 of the chip 10 when viewed in the chip width direction,and therefore the collet 30 can exert a force from just above the ridgeportion 15, i.e., from just above the light emitting point 16. Becauseof this, it is possible to improve the wetting of the solder at thelight emitting portion without exerting a large force. In other words,it is possible to improve the wettability of the solder at the lightemitting portion in an efficient manner Thus, when the chip 10 is joinedto the sub-mount 20, an excessive force is not necessary. In otherwords, when the chip 10 is mounted on the sub-mount 20, the chip 10 doesnot break, crack, or tilt. If the chip 10 tilts, the wetting becomesinsufficient. Then, the heat dissipation is deteriorated and thepolarization is deteriorated. Because this embodiment can prevent thechip 10 from tilting, it is possible to ensure the appropriatefunctioning of the semiconductor laser element at a high temperature,and provide a good polarization.

If the ridge portion 15 was formed on the line Pp that extends throughthe center of the p-type electrode 13 when viewed in the chip widthdirection, then the light emitting point would greatly be offset in thechip width direction (to the left in FIG. 1) from the point (line) ofthe force exerted on the chip 10 by the collet (i.e., from the line Pgextending through the center of gravity 17 of the chip 10, or from theline Pn extending through the center of the n-type electrode 14). Withsuch offset, it would be necessary to apply a large force onto the chip10 in order to ensure that the light emitting part of the chip 10becomes sufficiently wet by the solder. If the force applied onto thechip 10 was too small, the chip 10 would not become wet by the solder,and the heat dissipation of the chip 10 would drop.

In recent years, the chip of the semiconductor laser element tends tohave a longer cavity length (longer resonator length) and a shorter chipwidth in order to provide an increased output (high-power laser beam) ata reduced cost. For example, when the semiconductor laser element isdesigned to generate an optical output of 50 mW, the cavity length is800 μm and the chip width is 250 μm. On the other hand, when thesemiconductor laser element is designed to generate an optical output of150 mW, the cavity length is elongated to 2000 μm in order to enhancethe heat dissipation. In this example, if the number of chips to beobtained from a single wafer should be the same as the semiconductorlaser element that is designed to generate an optical output of 50 mW,then the chip width should be reduced to 100 μm. However, if the chipwidth is reduced for the semiconductor laser element having the inclinedsubstrate, the cross-sectional shape of the chip in a directionperpendicular to the resonator direction becomes similar to a diamondshape. Thus, the chip easily tilts, falls, collapses or break when aforce is applied onto the chip in order to join the chip to thesub-mount.

The side faces of the inclined substrate are cleavage planes. In case ofthe GaAs substrate, for example, the thickness of the inclined substrateis approximately 100 μm. If the thickness of the substrate is equal toor greater than, for example, 200 μm, the thickness of the substrate istoo large, and it is difficult to form the edge face (side face) bycleavage. On the other hand, if the thickness of the substrate is equalto or smaller than 50 μm, the thickness of the substrate is too small,and the substrate may crack during the mounting process, and the yieldmay drop. The drop of the yield results in an increase in cost.Therefore, the substrate thickness is approximately 100 μm.

As such, when the chip width becomes equal to or smaller than 150 μm,the cross-sectional shape of the chip takes a shape like a diamond, andthe above-mentioned problems are likely to occur. If the chip width isrepresented by W, the substrate thickness is represented by t, and theinclination angle of the substrate is represented by θ, then the widthof the chip that can receive a force from the collet is given by anequation of “W−t×tan θ.” If this width is smaller than the substratethickness t, the position of the center of gravity of the chip becomeshigh relative to the chip width. Thus, the chip becomes unstable to theforce applied from the collet in the vertical direction, i.e., the chipis easy to fall. As a result, a large force cannot be applied to thechip when the chip is joined to the sub-mount, if the chip has theabove-mentioned inclined substrate. Consequently, it becomes verydifficult to appropriately join the chip to the sub-mount. As the cavitylength of the chip becomes longer, the end faces of the chip becomedifficult to get wet with the solder as compared to the center area ofthe chip. Thus, it is necessary to apply a larger force onto the chip asthe cavity length of the chip is elongated. However, if the chip widthis small, the chip is easy to collapse or break. Specifically, if theratio of the cavity length L to the chip width W (L/W) is greater than10, then the chip is likely to collapse or break, and it is difficult tosufficiently join the chip 10 to the sub-mount 20 with an appropriateforce that ensures the good wetting to the solder.

On the other hand, the chip 10 of the semiconductor laser elementaccording to the above-described embodiment can improve or ensure thewetting to the solder with a relatively small force, as described above.Thus, when the chip 10 is joined to the sub-mount 20, it is notnecessary apply a large force onto the chip 10. As such, even if thechip 10 has the inclined substrate having a small width, the chip 10does not fall, collapse or break with the force applied from the top ofthe chip when the chip 10 is joined to the sub-mount 20. Therefore, thereliability of the semiconductor laser element is ensured, and thesemiconductor laser element can generate a high optical output(high-power laser beam) at a short wavelength.

Though the location of the ridge portion 15 in the chip width directionis on the line Pg that extends through the center of gravity 17 of thechip 10 in the above-described embodiment, the present invention is notlimited in this regard. For example, the location of the ridge portion15 in the chip width direction may be on the line Pn that extendsthrough the center of the n-type electrode 14 (or the center of thatsurface of the chip on which the n-type electrode 14 is disposed). Insuch instance, the collet 30 may approach (move downward to) the n-typeelectrode 14 along the line Pn to catch the chip 10. Then, the collet 30may apply a force onto the chip 10 (center of the n-type electrode 14)while keeping the contact between the collet 30 and the n-type electrode14 on the line Pn, thereby joining the chip 10 to the sub-mount 20. Whenthe collet 30 applies a force onto the chip 10 along the line Pn to jointhe chip 10 to the sub-mount 20, and the location of the ridge portion15 in the chip directions is on the line Pn, then the same advantages aswhen the collet 30 applies a force onto the chip 10 along the line Pgand the location of the ridge portion 15 in the chip directions is onthe line Pg are obtained.

Second Embodiment

A second embodiment of the present invention will be described below.

In the first embodiment, the semiconductor laser element has a singlelight emitting point. Thus, the semiconductor laser element of the firstembodiment is a single beam semiconductor laser element. The secondembodiment deals with a semiconductor laser element that has a pluralityof light emitting points. This laser element is a multi-beamsemiconductor laser element.

FIG. 6 illustrates a semiconductor chip 110 of a semiconductor laserelement according to the second embodiment. Similar components in thefirst and second embodiments are given similar reference numerals inFIGS. 1 and 6. In the following description, mainly the differencesbetween the first and second embodiments will be described.

The semiconductor chip (hereinafter simply referred to as “chip”) 110includes a p-type electrode 13 (p-type cladding layer), an n-typeelectrode 14, and a ridge portion 115 formed in the p-type electrode 13.The ridge portion 115 is a current constriction part that causes acurrent to concentrate and flow to the light emitting parts. The chip110 has two light emitting parts. In the second embodiment, the ridgeportion 115 includes two ridges (two protrusions) 115 a and 115 b,arranged spacedly from each other in the chip width direction.Accordingly, the points 116 a and 116 b are the light emitting points(parts) in the second embodiment.

The location of the first ridge 115 a of the ridge portion 115 is on theline P1, when viewed in the chip width direction, and the location ofthe second ridge 115 b of the ridge portion 115 is on the line P2. Thecenter line between the lines P1 and P2 is the line Pg that extendsthrough the center of gravity 17 of the chip 110, when viewed in thechip width direction. In other words, the center between the two lightemitting points 116 a and 116 b is just below the center of gravity 17of the chip 110 in the chip width direction. It should be noted that thecenter line between the lines P1 and P2 may not necessarily be the linePg. It is satisfactory as long as the center line between the lines P1and P2 extends on the right side of the center of the p-type electrode13.

In the second embodiment, therefore, it is satisfactory as long as thecenter line between the lines P1 and P2 extends on the right side of thecenter of the electrode that is joined to the sub-mount 20, or thecenter line between the lines P1 and P2 is offset from the center of theelectrode joined to the sub-mount 20 toward the center of the otherelectrode that is not joined to the sub-mount 20. Preferably, the centerline between the lines P1 and P2 extends between the lines Pp and Pn, orbetween the line Pp and a line in the vicinity of the line Pp.

As the second embodiment has the above-described structure, it ispossible to wet the chip 110 with the solder without applying a largeforce onto the chip 110, as in the first embodiment. Thus, it ispossible to appropriately join (mount) the chip 11 to the sub-mount 20without causing the chip 110 to fall, collapse or break. Therefore, evenwhen the multi-beam semiconductor laser element has an inclinedsubstrate having a relatively small width in the direction perpendicularto the cavity direction, it is still possible to mount the chip 110 ontothe sub-mount 20 in a desired manner. Accordingly, the reliability ofthe semiconductor laser element is ensured, and the semiconductor laserelement can generate a high optical output at a short wavelength.

In FIG. 6, the multi-beam semiconductor laser element has the two lightemitting points. The present invention is not limited in this regard.For example, the multi-beam semiconductor laser element may have threeor more light emitting points (i.e., three or more ridges). Each lightemitting point is associated with each ridge. In such instance, it issatisfactory if the center of the ridges is on the right side of thecenter of the p-type electrode 13 (or on the right side of the line Pp).For example, when the semiconductor laser element has three lightemitting points (i.e., three ridges) arranged at equal intervals in thechip width direction, then the position of the center ridge (secondridge) is between the line Pp (center of the p-type electrode 13) andthe line Pn (center of the n-type electrode 14). The position of thecenter ridge may be on the line Pg that extends through the center ofgravity 17 of the chip 110.

Third Embodiment

A third embodiment of the present invention will be described below.

In the first and second embodiments, the current constriction part hasthe ridge structure that appears on the outer surface of the substrateor the chip. In the third embodiment, the ridge structure of the currentconstriction part is embedded in the chip.

FIG. 7 is a cross-sectional view of a semiconductor chip 210 of asemiconductor laser element according to the third embodiment. Similarreference numerals are used in the first and third embodiment todesignate similar components in FIGS. 1 and 7. In the followingdescription of the third embodiment, mainly the differences between thefirst and third embodiments will be described.

The semiconductor chip (hereinafter simply referred to as “chip”) 210includes a current constriction part 220 having a built-in structure oran embedded structure. The built-in structure is a structure in whichoutside areas along a current path of the injection current (elongatedarea) are recessed by an etching process, and other semiconductor layersare stacked in the recesses (concave areas). A method of manufacturingthe chip 210 will be described below.

Firstly, a p-type cladding layer (e.g., p-AlGaInP layer) 221 is formedon the lower surface of the substrate 210, and the p-type cladding layer221 is etched except for an elongated area, which corresponds to a ridgehaving, for example, an approximately 2 μm width. On both sides of theelongated area, are formed the concave areas. Subsequently, an n-typebuilt-in layer (e.g., n-AlInP layer) 222 is grown in each of the concaveareas (on along the ridge area on both sides of the ridge area) by aMOCVD method. The built-in layers serve as current blocking layers. Theridge area is covered with an insulation film such that no crystal forthe built-in layer 222 is grown on the ridge area. Thus, the height ofthe ridge area becomes equal to the height of the neighboring areaswhere the built-in layers are formed.

After that, the p-type built-in layer (e.g., p-GaAs layer) 223 is grownby the MOCVD method. The p-type built-in layer 223 serves as a contactlayer. The built-in layer 223 is crystal grown over the entire surfaceof the ridge area and the neighboring areas (layer 222) such that thesurface of the built-in layer 223 becomes substantially flat.Subsequently, an insulation film 224 is formed by a CVD method. In orderto provide an electric contact, part of the insulation film 224 belowthe ridge is etched to form a current injection part. The currentconstriction part 220 is formed in this manner. Then, the p-typeelectrode 13 is formed over a stack of these semiconductor layers 221 to224. In the chip 210 of the third embodiment, therefore, the ridge isembedded (enclosed) in the crystal.

The location of the ridge of the current constriction part 220 in thechip width direction is on the line Pg that extends through the centerof gravity 17 of the chip 210, as shown in FIG. 7. Thus, the lightemitting point 16 is present just below the center of gravity 17 of thechip 210 when viewed in the chip width direction. It should be notedthat the location of the light emitting point 16 (or the location of theridge) is not limited to the location shown in FIG. 7. It issatisfactory as long as the ridge of the current constriction part 220is formed on the right side of the center of the p-type electrode 13joined to the sub-mount 20 (or on the right side of the center of thechip 210 on which the p-type electrode 13 is provided).

In this embodiment, therefore, the location of the ridge of the currentconstriction part 220 is on the right side of the line Pp that extendsthrough the center of the p-type electrode 13. Preferably, the locationof the ridge of the current constriction part 220 is between the line Ppthat extends through the center of the p-type electrode 13 and the linePn that extends through the center of the n-type electrode 14 (or a linein the vicinity of the line Pn).

Because the semiconductor laser element of the third embodiment has theabove-described configuration, it is possible to wet the chip 210 withthe solder without applying a large force onto the chip 210. This issimilar to the first and second embodiments. In the third embodiment, itis also possible avoid the falling and collapsing of the chip 210 when ajoining force is applied onto the chip 210. Thus, the chip 210 is joinedto the sub-mount 20 in a desired manner. As such, the semiconductorlaser element having the current constriction part, in which the ridgeis embedded, can appropriately be joined to the sub-mount 20 even if theinclined substrate of the semiconductor laser element (chip 210) has arelatively small width in a direction perpendicular to the cavitydirection. Accordingly, the reliability of the semiconductor laserelement is ensured, and the semiconductor laser element can generate ahigh optical output at a short wavelength.

Fourth Embodiment

A fourth embodiment of the present invention will be described below.

In the third embodiment, the semiconductor laser element has thebuilt-in current constriction part. The semiconductor laser element ofthe fourth embodiment has another type of current constriction part.

FIG. 8 is a cross-sectional view of an exemplary semiconductor chip 310of a semiconductor laser element according to the fourth embodiment ofthe present invention. Similar reference numerals are used in the firstand fourth embodiments. In the following description, the differencebetween the chip 10 of the first embodiment and the chip 310 of thefourth embodiment will mainly be described.

The semiconductor chip (hereinafter simply referred to as “chip”) 310has a current constriction part 320. The current constriction part 320is formed by patterning an insulation film and a crystal-made contactlayer. A method of manufacturing the chip 310 will be described below.

Firstly, a p-type cladding layer (e.g., p-AlInP layer) 321 is formed onthe lower surface of the substrate 11, and a p-type contact layer (e.g.,p-GaAs layer) 322 is formed on the p-type cladding layer 321. Then, thecontact layer 322 is etched to leave a current constriction area(elongated area) having, for example, an approximately 40 μm width, asshown in FIG. 8. Subsequently, an insulation film 323 is formed by a CVDmethod. In order to provide an electric contact, part of the insulationfilm 323 is etched and a current injection part is formed. The currentconstriction part 320 is formed in this manner. The chip 310 has a lightemitting point (light emitting part) 316. The width 316 d of the lightemitting part 316 corresponds to the width of the current constrictionarea (e.g., approximately 40 μm).

The center of the current constriction area of the current constrictionpart 320 in the chip width direction is on the line Pg that extendsthrough the center of gravity 17 of the chip 310. Thus, the center ofthe light emitting part 316 is just below the center of gravity 17 ofthe chip 310, when viewed in the chip width direction. It should benoted that it is satisfactory as long as the center of the currentconstriction area (light emitting part) is on the right side of thecenter of the electrode (13) that is joined to the sub-mount. In otherwords, it is satisfactory as long as the center of the currentconstriction area (light emitting part) 316 is offset from the center(Pp) of the electrode (13) that is joined to the sub-mount toward thecenter (Pn) of the other electrode (14) that is not joined to thesub-mount.

In the illustrated embodiment, the structure of the current constrictionpart 320 is decided such that the center position of the currentconstriction area of the constriction part 320 is on the right side ofthe line Pp that extends through the center of the p-type electrode 13.Preferably, the center of the current constriction area is between theline Pp that extends through the center of the p-type electrode 13 andthe line Pn that extends through the center of the n-type electrode 14(or a line in the vicinity of the line Pn).

Because the semiconductor laser element of the fourth embodiment has theabove-described configuration, it is possible to wet the chip 310 withthe solder without applying a large force onto the chip 310. This issimilar to the first, second and third embodiments. In the fourthembodiment, it is also possible avoid the falling and collapsing of thechip 310 when a joining force is applied onto the chip 310. Thus, thechip 310 is joined to the sub-mount 20 in a desired manner. As such, thesemiconductor laser element having the current constriction part 320, inwhich no ridge is directly associated with the light emitting part, canappropriately be joined to the sub-mount 20 even if the inclinedsubstrate of the semiconductor laser element (chip 310) has a relativelysmall width in a direction perpendicular to the cavity direction.Accordingly, the reliability of the semiconductor laser element isensured, and the semiconductor laser element can generate a high opticaloutput at a short wavelength.

Modifications

In each of the above-described embodiments, the inclined substrate 11 isa GaAs substrate. The present invention is not limited in this regard.For example, the inclined substrate 11 may be an InP substrate, a GaNsubstrate, or an Si substrate. The material of the inclined substrate 11may be decided depending upon the wavelength of the light to begenerated (emitted) from the semiconductor laser element.

In each of the above-described embodiments, the chip 10 (110, 210, 310)is mounted on the sub-mount 20 by the junction down method. The presentinvention is not limited in this regard. For example, the chip 10 (110,210, 310) may be mounted on the sub-mount 20 by a junction up method. Itshould be noted that the junction down method is preferred if the heatdissipation is taken into account because the heat is more released fromthe chip when the chip is joined to the sub-mount by the junction downmethod.

In each of the above-described embodiments, the center of the p-typeelectrode 13 coincides with the center of that face of the chip on whichthe p-type electrode 13 is formed (i.e., the center of the lower face ofthe chip) when viewed in the chip width direction, and the center of then-type electrode 14 coincides with the center of the opposite face ofthe chip on which the n-type electrode 14 is formed (i.e., the center ofthe upper face of the chip) when viewed in the chip width direction. Thepresent invention is not limited in this regard. For example, the centerof the p-type electrode 13 may be offset from the center of the lowerface of the chip when viewed in the chip width direction, and/or thecenter of the n-type electrode 14 may be offset from the center of theupper face of the chip. With such configuration, the center position ofthe current constriction part(s) or the current constriction area in thechip width direction is offset from the center of that surface of thechip which is joined to the sub-mount 20 toward (or beyond) the centerline of the opposite surface of the chip. Then, such configuration canhave the same advantages as the first embodiment.

In the first, third and fourth embodiments, the collet 30 approaches thechip 10 along the line Pg, and catches the chip 10 (FIG. 3). Then, thecollet 30 applies the force X3 to the chip 10 along the line Pg when thecollet 30 joins the chip to the sub-mount 20 because the light emittingpoint (current constriction part) is present on the line Pg. Thus, thecollet 30 can apply the force to the chip 10 from just above the lightemitting point. The present invention is not limited in this regard. Forexample, if the light emitting point is not present on the line Pg, buton the line Pp, the collet 30 may move to the line Pp after placing thechip 10 on the sub-mount 20. Upon reaching the line Pp, the collet 30may apply the force to the chip 10 such that the collet 30 applies theforce from just above the light emitting point. By moving the collet 30in this manner after placing the chip 10 on the sub-mount 20, the collet30 can apply the force to the chip 10 from just above the currentconstriction part. In this instance, when the collet 30 catches andholds the chip 10, the collet 30 approaches along the line Pg andcatches the chip 10. The collet 30 carries the chip 10 to the sub-mount20, and moves to the line Pp after placing the chip 10 on the sub-mount20. This modification also brings about the same advantages as the firstembodiment. In this manner, it is possible to join the chip to thesub-mount in a desired manner regardless of the location of the lightemitting point.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the present invention. The novel apparatuses (devices,elements) and methods described herein may be embodied in a variety ofother forms; furthermore, various omissions, substitutions and changesin the form of the apparatuses (devices, elements) and methods describedherein may be made without departing from the gist of the presentinvention. The accompanying claims and their equivalents are intended tocover such forms or modifications as would fall within the scope andgist of the present invention.

The present application is based upon and claims the benefit of apriority from Japanese Patent Application No. 2015-181579, filed Sep.15, 2015, and the entire contents of which are incorporated herein byreference.

What is claimed is:
 1. A semiconductor laser element comprising: asemiconductor chip, the semiconductor chip including: a substrate havingfour side faces, a top face and a bottom face, with two side faces ofthe four side faces being inclined side surfaces which face each otherin a first direction, and another two side faces being vertical sidesurfaces which face each other in a second direction, the seconddirection being perpendicular to the first direction, each said verticalside surface having a parallelogram shape; a semiconductor layer formedon one of the top and bottom faces of the substrate, the semiconductorlayer having a multi-layer structure including at least an active layer;a first electrode formed on the other of the top and bottom faces of thesubstrate; a second electrode formed on the semiconductor layer, one ofthe first electrode and the second electrode being joined to a sub-mountwhen the semiconductor laser element is assembled in a laser device; anda current constriction part formed in the semiconductor layer, thecurrent constriction part being configured to cause a current toconcentrate and flow to a particular area of the active layer, alocation of the current constriction part in the first direction beingoffset from a center of one of the top and bottom faces of the chip, onwhich one of the first and second electrodes to be joined to thesub-mount is formed, toward a center of the other of the top and bottomfaces of the chip, when viewed in the first direction.
 2. Thesemiconductor laser element according to claim 1, wherein the locationof the current constriction part in the first direction is on a linethat extends through a center of gravity of the semiconductor chip whenviewed in the first direction.
 3. The semiconductor laser elementaccording to claim 1, wherein the location of the current constrictionpart in the first direction is on a line that extends through a centerof one of the top and bottom faces of the chip on which one of the firstand second electrodes not to be joined to the sub-mount is formed whenviewed in the first direction.
 4. The semiconductor laser elementaccording to claim 1, wherein the current constriction part has a ridgestructure.
 5. The semiconductor laser element according to claim 4,wherein the current constriction part has a ridge structure that appearson an outer surface of the semiconductor chip.
 6. The semiconductorlaser element according to claim 4, wherein the current constrictionpart has a ridge structure that is embedded in the semiconductor chip.7. The semiconductor laser element according to claim 5, wherein thecurrent constriction part has a plurality of ridges arranged in thefirst direction, and a center position of said plurality of ridges inthe first direction is the location of the current constriction part inthe first direction.
 8. The semiconductor laser element according toclaim 6, wherein the current constriction part has a plurality of ridgesarranged in the first direction, and a center position of said pluralityof ridges in the first direction is the location of the currentconstriction part in the first direction.
 9. The semiconductor laserelement according to claim 6, wherein the current constriction part hasa single ridge, and a position of ridge in the first direction is thelocation of the current constriction part in the first direction. 10.The semiconductor laser element according to claim 1, wherein the firstelectrode is an electrode not to be joined to the sub-mount, and thesecond electrode is an electrode to be joined to the sub-mount.
 11. Thesemiconductor laser element according to claim 1, wherein the firstdirection is a width direction of the substrate.
 12. The semiconductorlaser element according to claim 1, wherein the location of the currentconstriction part in the first direction is between the center of one ofthe top and bottom faces of the chip, on which one of the first andsecond electrodes to be joined to the sub-mount is formed, and thecenter of the other of the top and bottom faces of the chip, when viewedin the first direction.
 13. A method of manufacturing a semiconductorlaser element, comprising: preparing a substrate, the substrate havingfour side faces, a top face and a bottom face, with two side faces ofthe four side faces being inclined side surfaces which face each otherin a first direction, and the other two side faces being vertical sidesurfaces which face each other in a second direction, the seconddirection being perpendicular to the first direction, each said verticalside surface having a parallelogram shape; forming a semiconductor layeron one of the top and bottom faces of the substrate, the semiconductorlayer having a multi-layer structure including at least an active layer;forming a first electrode formed on the other of the top and bottomfaces of the substrate; forming a second electrode formed on thesemiconductor layer; and forming a current constriction part formed inthe semiconductor layer, the current constriction part being configuredto cause a current to concentrate and flow to a particular area of theactive layer, a location of the current constriction part in the firstdirection being offset from a center of one of the top and bottom facesof the chip, on which one of the first and second electrodes to bejoined to the sub-mount is formed, toward a center of the other of thetop and bottom faces of the chip, when viewed in the first direction.14. A method of manufacturing a semiconductor laser device comprising:preparing a semiconductor laser element according to claim 1; placingthe semiconductor laser element on the sub-mount such that one of thefirst and second electrodes contacts or faces the sub-mount; andapplying a force onto the semiconductor laser element in a directionperpendicular to a joining plane between said one of the first andsecond electrodes and the sub-mount so as to join the semiconductorlaser element to the sub-mount.
 15. A method of manufacturing asemiconductor laser device comprising: preparing a semiconductor laserelement, the semiconductor laser element including a substrate, asemiconductor layer, a first electrode, a second electrode, and acurrent constriction part, the substrate having four side faces, a topface and a bottom face, with two side faces of the four side faces beinginclined side surfaces which face each other in a first direction, andthe other two side faces being vertical side surfaces which face eachother in a second direction, the second direction being perpendicular tothe first direction, each said vertical side surface having aparallelogram shape, the semiconductor layer being formed on one of thetop and bottom faces of the substrate, the semiconductor layer having amulti-layer structure including at least an active layer, the firstelectrode being formed on the other of the top and bottom faces of thesubstrate, the second electrode being formed on the semiconductor layer,the current constriction part being formed in the semiconductor layer,the current constriction part being configured to cause a current toconcentrate and flow to a particular area of the active layer; placingthe semiconductor laser element on a sub-mount such that one of thefirst and second electrodes contacts or faces the sub-mount; andapplying a force onto the semiconductor laser element in a directionperpendicular to a joining plane between said one of the first andsecond electrodes and the sub-mount from above the current constrictionpart, so as to join the semiconductor laser element to the sub-mount.